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EOL Seminar

Evaluating the Characteristics of Hail through Field Observations and Unique Measurement Systems

Ian M. Giammanco

IBHS Research Center

Severe hail events have resulted in annual property losses exceeding $1 billion dollars. In an effort to understand the fine-scale damage modes associated with hail impacts on various materials information is needed regarding the characteristics and material properties of hail.

Throughout historical literature anecdotal or visual observations have been used to describe the hardness property of hailstones (e.g. hard, slushy, etc...). Little historical research exists describing the material properties of hail and standardized tests have focused only on duplicating hailstone impact kinetic energy. A unique test device was designed and built in order to perform a compressive strength test on hailstones measured in the field. The device applies a compressive load to a hailstone and integrates a fast response load-cell and associated data acquisition hardware to measure the applied force through the point of fracture. The strain-rate applied to the stone is fast enough to produce a brittle failure and the peak compressive force is appropriately scaled to produce an estimate of the compressive stress. The compressive strength is used as a proxy to represent the material hardness of hailstones.

In addition to the material properties of hail, information is needed regarding the time history of hail size distributions within thunderstorms for both meteorological, risk modeling, and engineering applications. While disdrometer measurement systems have existed for some time, they are often costly and difficult to apply in an adaptive observing framework. A rapidly deployable hail impact disdrometer was developed using low-cost microcontroller technology and piezo-electric sensors to achieve high sampling rates (>500 Hz) in order to effectively capture hail impacts. Two prototypes were developed for testing in 2014. The relatively simple design and low cost will allow for a deployable network to be developed.